<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <!-- 
        让你代码飞起来。
        div>ul>li

        div+div

        ul>li*10

        div.box
        div#box
     -->

     <div class="box"></div>
     <div id="item"></div>
</body>
</html>